\[
\begin{aligned}
J_\nu(\vec{p}) &= \frac{1}{4\pi}\oint_\mathbb{S^2} I_\nu(\vec{p},\hat{\omega}) \mathop{d \hat{\omega} } \\
&\vec{p} \in \mathbb{R}^3, \hat{\omega} \in \mathbb{S}^2\\
\end{aligned}
\]
- Specific intensity and its first moment.
- 4 and 6 dimensional functions!